Copper plating bath and process



United States Patent 2,696,467 1'. r I 1; CIOPPERPLA'IING BATH AND PROCESS Dwight M. Overcash, Elyria, and Richard B. Parks, Lorain, Ohio, assignors to General Motors Corporation, Detroit, Mich, a corporation of Delaware No Drawing. Application January 4, 1952,

Serial No. 265,054

13 Claims. (Cl. 204-52) This invention has to do with electrodeposition of metals and is more particularly concerned with electrodepositionof copper.

agents in novel relationship and the determination of the factors alfecting the action of these agents to produce most satisfactory results.

I The'pr'esent invention broadly has to do withv the addition of a small proportion of lignin sulfonic acid or ligninsulfonates to aqueous acid copper plating baths containing a small proportion of thiourea or derivative th'ereof.

Since cost and commercial availability will, of course, .be factors in determining the particular thiourea compound to be used and since thiourea, per se, CS(NI-Iz)z is'suit'able from all standpoints, it is at present'preferred forp'lantuse; However, other compounds may be used which also have the following nucleus typical of thiourea parse:

The inclusion of lignin sulfonic acid orsalts thereof in 'an acid copper plating bath containing thiourea or derivatives thereof extends the plating range at both high and low current density ends. This property is very important, especially the ability to plate atlow current densities. Conventional acid copper plating baths have the inherent property of low efficiency at low' current densities. .As a :consequence, parts with recesses are .diflicult to plate.v By additions of thiourea'or derivatives thereof, and lignin sulfonic acid or salts thereof, it is possible to plate parts with uniformly brightor smooth copper even though the parts have recesses therein.

' For best results the bath; of the present invention also contains organic compounds of the class known as surface tension reducing or wetting agents. The preferred wetting agent is an anionic wetting agent of the alkyl aryl sulfonate type,having from to 15 carbon atoms the alkyl chain, typical compounds of this class having the following chemical structures:

2,696,467 Patented Dec. 7,1954

SOsNa Potassium or hydrogen may be substituted for sodium in the foregoing illustrative chemical structures l to 6 inclusive. Wetting agents having the structures of the formulas l to 6 above are available commercially under the trade-name Oronite.

While wetting agents having the above structural formulas give superior results as compared with other Wetting agents, it is within the scope of the invention in its broader aspects to employ other organicwetting agents. Many of the wetting agents found suitable are aromatic sulfonates and a considerable number are on the market under various trade-names. Among those other wetting agents found suitable, the following are typical:

Triton 720 Neomerpin Tergitol 08 'Duponol Triton 720 is a sulfonated ether having a branched chain and an aromatic nucleus. More specifically Triton 720 is one or more compounds of the formula:

wherein Ar is a hydrocarbon substituted aromatic nucleus, M is a metal of the group consisting of sodium, potassium, calcium and magnesium, or is ammonia or an amine group, n is any whole number from three to six and the hydrocarbon substituent of the aryl group has carbon atoms in the range of four to twelve. The Neomerpin compounds are alkyl naphthalene sulfonic acids and sodium salts thereof. Tergitol 08 is a sodium secondary alcohol sulfate. The Duponol materials are sodium salts of sulfonated higher aliphatic alcohols, sodium lauryl sulfate being a typical example.

The composition of the bath exclusive of the novel addition agentsis of standard character. For example, aqueous solutions containing 15 to 4.0 ounces of copper sulfate (CuSO4.5HzO) and sulfuric acid (66 B.) within the range of 3 to 15 ounces per gallon may be used.

The amount of thiourea or derivative of thiourea in the bath in general is the same as in; known acid copper plating baths containing thiourea as a brightener; for example, in an amount or amounts as described in Phillips and Clifton Patent 2,563,360 and Chevis applicationSerial No. 127,521, filed November 15, 1949, bothof which are assigned to the assignee of this application. As little as about .0003 oz. per gallon, of thiourea or derivative will bring about a noticeable improvement in brightness and structure. Much larger additions up to above .67 oz. per gallon have been employed but the larger amounts are unnecessary for best results. In most instances therefore, the thiourea or thiourea derivative employed is within the range of .001 to .050 oz. per gallon of solution. A preferred range is .002 t'o .005 oz.

per gallon. The inclusion of the lignin sulfonic acid or salts thereof makes the bath less sensitive to additions of thiourea or derivatives thereof.

The proportion of lignin sulfonic acid or salts thereof in the bath may range from as little as .001 oz. per gallon up to about ,5 oz. per gallon. The higher amounts tend to cause dulling of the copper. In commercial applications about .01 to .05 oz. of lignin sulfonic acid or salts thereof usually are employed per gallon of plating solution.

The concentration of the wetting agent also is on the same order as, employed in acid copper plating baths containing thiourea as described in Phillips and Clifton Patent 2,563,360 and in Chevis application Serial No. 127,521, filed November 15, 1949. The amount of wetting agent may range, for example, from about .001 to .6 oz. per gallon of solution. In commercial applications it is common to employ around .01 to .02 oz. per gallon of so1ution.

Small amounts of such materials as O-benzoic sulfimide, sodium O-benzoic sulfimide, molasses, beta-naphthol, alpha-naphthol, itaconic acid, citraconic acid and messiconic acid may be added to the bath, if desired. Moreover, we have found that it is beneficial in many instances to employ a bath containing a trace of chloride ion, such as that which may be contributed by the addition of a very small amount of hydrochloiic acid. While hydrochloric acid may be beneficially used in quantities ranging from 0.005 to 0.1 oz. of the commercially concentrated acid per gallon of bath in various applications, excessive amounts of the chloride ion tend to detrimentally effect the brightness of the copper deposits.

The following are typical and illustrative examples of copper plating baths or electrolytes in accordance with the invention in which the described quantities of the named ingredients are present per gallon of aqueous solution.

Example 1 28 02. copper sulfate (CuSO4.5H2O) see. of 66 B. commercial sulfuric acid .005 oz. thiourea .02 oz. lignin sulfonic acid.

Example 2 Same as Example 1 except that the solution also contains .01 ounce of alkylaryl sulfonate wetting agent having from 10 to 15 carbon atoms in the alkyl chain.

7 I Example 3 same as Example 1 except that thiosemicarbazide is employed in place of thiourea.

Example 4 Same as Example 2 except that thiosemicarbazide is employed in place of thiourea.

Example 5 Same as Example 1 except that thiosinamine is employed in place of thiourea;

Example 6 Same as -Exarnple 2 except that thiosinamine is employed in place of thiourea.

Example 7 1 Same as Example 1 except that acetyl thiourea is employed in place of thiourea.

Example 8 Same as Example 2 except that acetyl thiourea is employed in place of thiour'ea.

Example 9 Sameas' Example 1 except that the solution also contains .01 oz. of sodium lauryl sulfate.

Example 10 S ame as Example 1 except that the solution also contains .01 oz. of T'ergitol 08.

Example 11 as fixamplel except that the semen contains .01 oz. of Triton 720.

l Example 12 Same as Example 1 except that the sodiilm, calcium, magnesium or potassium salt of lignin sulfonic acid is employed in place of the acid.

Example 13 Same as Example 2 except that the sodium, calcium, magnesium orpotassium salt of lignin sulfonic acid is employed in place of the acid.

Example 14 15 to 40 02. copper sulfate (CuS OLSHEG), 3 to 15 oz. (66 B.) sulfuric acid, .001 to .050 oz. thionrea, and .001 to .5 oz. lignin sulfonic acid.

Example 15 Same as Example 14 except that .001 to .6 oz. organic wetting agent is added.

Example 16 Same as Example 14 except that to oz doinmercially concentrated hydrochloric acid is added.

Example 17 Same as Example 15 except that the solution has added thereto about .01 to .1 gram of any one of o -bje'nzoic' sulfimide, sodium o-benzoic sulfimide, betanaplitli'dl, alphanaphthol, itaconic acid, citraconic acid, n'ie'ssiconic and molasses.

. Example 18 Same as Example 1 except that .01 to .02 oz. of a wetting agent having the chemicalstructure' (l), (2), (3), (4), (5), or (6) above is added. 4 I

The bath temperature may vary considerably, satisfactory deposits having been obtained at temperatures Within the range of 40 130 F. In large scale production operations, because of the simplicity, it is preferred to operate at or near room temperature, for example, 75 F. or thereabout. Current densities of 5 to amperes per square foot of cathode area have been employed s ecessfully. Higher current densities require better agitation of the solution. Agitation may be accomplished by forcing air through the solution, by rapid movement of the cathode, by pumping solution from the plating tank and pumping it back into the tank adjacent the cathode, etc.

Articles plated with bright copper by the process and bath of this invention may be readily electroplated with other metals such as bright nickel and/or chromium. Usually the nickel and/or chromium are plated in the bright form which require little or no hufling.

While I have described preferred embodiments of my invention, it will be understood that changes and modifications may be made without departing from the principles of my invention.

I claim: 7,

1. An electrolyte for electrodeposition of copper consisting essentially of an aqueous copper sulfate solution containing free sulfuric acid and to which has added a compound having the nucleus in an amount within the range of .0003 to .67 ounce per gallon of solution and an ingredient selected from the class consisting of lignin sulfonic acid and salts of lignin sulfonic acid in an amount within the range of .001 to .5 ounce per gallon of solution.

2. A copper plating bath as in claim 1 to which has been added .001 to .6 ounce of an organic wetting agent per gallon of solution.

3. A copper plating bath as in claim 1 to Which has been added an anionic Wetting agent having the following chemical structure in an amount within the range of .001 to .6 oz. per gallon of solution:

03M in which R represents an alkyl group having 10 to 15 carbon atoms and M represents sodium, potassium or hydrogen.

4. An electrolyte for electrodeposition of copper consisting essentially of an aqueous solution of copper sulfate, sulfuric acid, a material of the class consisting of thiourea and derivatives thereof, and a material of the class consisting of lignin sulfonic acid and salts thereof, the copper sulfate being present in an amount within the range of 15 to 40 ounces per gallon of solution, the sulfuric acid (66 B.) within the range of 3 to 15 ounces per gallon, the material of the class consisting of thioureas and derivatives thereof in an amount within the range of .001 to .050 ounce per gallon of solution and the material of the class consisting of lignin sulfonic acid and salts thereof in an amount within the range of .001 to .5 ounce per gallon of solution.

5. An electrolyte as in claim 4 to which has been added an anionic wetting agent having the following chemical structure in an amount within the range of .001 to .6 oz. per gallon of solution:

in which R represents an alkyl group having to carbon atoms and M represents sodium, potassium or hydrogen.

6. An electrolyte for electrodeposition of copper consisting essentially of an aqueous solution of copper sulfate, sulfuric acid, thiourea, and lignin sulfonic acid, the copper sulfate being present in an amount within the range of 15 to 40 ounces per gallon of solution, the sulfuric acid (66 B.) within the range of 3 to 15 ounces per gallon, the thiourea in an amount within the range of .001 to .050 ounce per gallon of solution and the lignin sulfonic acid in an amount within the range of .001 to .5 ounce per gallon of solution.

7. An electrolyte for electrodeposition of copper consisting essentially of an aqueous solution of copper sulfate, sulfuric acid, thiourea, and lignin sulfonic acid, the copper sulfate being present in an amount within the range of 15 to 40 ounces per gallon of solution, the sulfuric acid (66 B.) within the range of 3 to 15 ounces per gallon, the thiourea within the range of .001 to .050 ounce per gallon of solution and the lignin sulfonic acid in an amount within the range of .001 to .5 ounce per gallon of solution, said solution having had added thereto an anionic wetting agent having the following chemical structure in an amount within the range of .001 to .6 oz. per gallon of solution:

in which R represents an alkyl group having 10 to 15 carbon atoms and M represents sodium, potassium or hydrogen.

8. An electrolyte for electrodeposition of copper consisting essentially of copper sulfate, sulfuric acid, thiourea, lignin sulfonic acid, and an ionic wetting agent having the following chemical structure:

in which R represents an alkyl group having 10 to 15 carbon atoms and M represents sodium, potassium or hydrogen, the copper sulfate being present in an amount within the range of 15 to 40 ounces per gallon of solution, the sulfuric acid (66 B.) within the range of 3 to 15 ounces per gallon of solution, the thiourea within the range of .002 to .005 ounce per gallon of solution, the lignin sulfonic acid within the range of .01 to .02 ounce per gallon of solution and the wetting agent within the range of .01 to .02 ounce per gallon of solution.

9. An electrolyte for electrodeposition of copper consisting essentially of copper sulfate, sulfuric acid, a material of the class consisting of thiourea and derivatives thereof, a material of the class consisting of lignin sulfonic acid and salts thereof, and an ionic wetting agent having the following chemical structure:

in which R represents an alkyl group having from 10 to 15 carbon atoms and M represents sodium, potassium or hydrogen, the copper sulfate being present in an amount Within the range of 15 to 40 ounces per gallon, the sulfuric acid (66 B.) within the range of 3 to 15 ounces per gallon of solution, the material of the class consisting of thiourea and derivatives within the range of .002 to .005 ounce per gallon of solution, the material of the class consisting of lignin sulfonic acid and salts thereof within the range of .01 to .05 ounce per gallon of solution and the Wetting agent within the range of .01 to .02 ounce per gallon of solution.

10. A method of electrodepositing copper which comprises passing electric current from an anode to a cathode through the plating bath defined in claim 1.

11. A method of electrodepositing copper which comprises passing electric current from an anode to a cathode through the plating bath defined in claim 7.

12. An electrolyte for electrodeposition of copper comprising essentially an aqueous copper sulfate solution containing free sulfuric acid and to which has added a compound having the nucleus References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,544,726 Colcord July 7, 1925 2,195,409 Flett Apr. 2, 1940 2,391,289 Beaver Dec. 18, 1945 2,489,538 Phillips et a1. Nov. 29, 1949 

1. AN ELECTROYTE FOR ELECTRODEPOSITION OF COPPER CONSISTING ESSENTIALLY OF AN AQUEOUS COPPER SULFATE SOLUTION CONTAINING FREE SULFURIC ACID AND TO WHICH HAS ADDED A COMPOUND HAVING THE NUCLEUS 